In order to store data of 2 or more bits, conventional non-volatile memory devices include 4-level non-volatile memory cells, each having 4 threshold voltage levels, or 8-level non-volatile memory cells, each having 8 threshold voltage levels. Since a 4-level non-volatile memory cell is programmed using four threshold voltage levels, the 4-level non-volatile memory cell is able to store 2-bit data. Since an 8-level non-volatile memory cell is programmed using eight threshold voltage levels, the 8-level non-volatile memory cell is able to store 3-bit data.